Flare stack with a liquid seal



Dec. 7, 1965 H. H. WALL, JR 3,222,259

I FLARE STACK WITH A LIQUID SEAL Filed 001;. 25, 1963 2 Sheets-Sheet 1 FIG. 3

1965 H- H. WALL. JR 3,222,259

FLARE STACK WITH A LIQUID SEAL Filed 001;. 25, 1965 2 Sheets-Sheet 2 FIG. 4

United States Patent M 3,222,259 FLARE STACK WITH A LIQUID SEAL Henry H. Wall, Jr., Baton Rouge, La., assignor to Ethyl Corporation, New York, N.Y., a corporation of Virginia Filed Oct. 25, 1963, Ser. No. 319,930 4 Claims. (Cl. 196-46) This invention relates to a novel liquid seal flamearresting discharge head for use in combination with a flare stack, especially to a water-free seal for such use and is a continuation-in-part of my copending application, Serial Number 53,246, filed August 31, 1960, now abandoned.

In present refinery and petrochemical plants it is common practice to provide a flare system for safe disposal of excess quantities of flammable vapors. Such a flare system consists of manual and automatic pressure relief equipment, collecting lines, a header, a flare stack, and a sealing device between the header and stack to prevent back flow of flame into the system in the event that the flow of flammable vapors is stopped.

At present, sealing is effected by the use of flame arrestors or by the use of liquid seals. Flame arrestors always present pluggage problems and have the disadvantages of unreliability for stopping detonations. In present liquid seal devices it is generally desirable to employ water as the sealing medium. This is extremely undesirable in many situations but cannot be avoided because of the nature and design of present sealing devices. Thus, where water is employed as the liquid seal in present devices it presents problems in extremely cold climates in that adequate measures must be taken to prevent freezing of the water both in the seal of the device and in the flare stack. Further, water presents a severe corrosion problem when handling water-soluble acid vapors.

On the other hand, where a hydrocarbon fluid is employed as the sealing fluid in present devices this presents further flammability problems and alsoproduces considerable loss of the hydrocarbon fluid. Thus, even where a low flash point fluid such as kerosene is employed, and in an environmentwhere there is little danger of its being ignited from a flashback, its positive vapor pressure prevents its use because if used this would result in a gradual level loss due to evaporation inasmuch as the gases must pass therethrough. But even should one employ a low flash point hydrocarbon in present devices an additional acute disadvantage results. Thus, where a low flash point hydrocarbon is employed, as for example kerosene,.there exists in addition to the normal flammability hazard the possibility of a vapor surge which would cause the seal liquid to be blown out of the sealing device and out of the stack.

Because of these and other disadvantages it is an object of the present invention to provide a new and improved seal device for use in combination with a flare stack, particularly one employing a liquid hydrocarbon seal fluid. In particular, it is an object of the present invention to provide such a device which offers the advantages of a liquid seal without the disadvantages of evaporation loss or flammability hazards such as caused by cessation of vapor flow or that caused by slugging due to sudden vapor surges.

The invention is better understood by referring to the drawings in which FIGURE 1 shows a liquid seal device under no-flow conditions;

FIGURE 2 shows a liquid seal device under normal flow conditions; and

3,222,259 Patented Dec. 7, 1965 FIGURE 3 shows a liquid seal device when there occurs a malfunction of the check valve; and

FIGURE 4 shows the liquid seal device installed in combination with a flare stack.

The foregoing and other objects are achieved in accordance with the present invention providing a new and novel flame-arresting discharge head for combustible vapors for use in combination with a flare stack. The flame-arresting discharge head comprises a liquid seal drum with a vapor discharge opening at its upper portion, a liquid seal loop trap opening into the lower portion of the drum, a vapor supply loop extending through the bottom of the drum and opening within the drum at a height above that at which the liquid seal trap opens so that the opening of the vapor supply loop is not covered by liquid from the liquid trap, the vapor supply loop extending downwardly from the bottom of the seal drum and joining the liquid seal loop trap at a branched connection, one branch extending downwardly for a distance and then upwardly to form the liquid seal trap loop and the other branch extending laterally for connection to a vapor supply above the level of the bottom of the seal drum, and a check valve closing the opening of the vapor supply loop within the seal drum against downward passage of flame and permitting uuward travel of vapor through the last-mentioned opening only when the vapor is supplied under a pressure suflicient to open the check valve, said pressure being also suflicient to expel the trap liquid from the portion of the vapor supply loop above the branched connection, the liquid seal trap loop extending far enough below the branched connection so that liquid remains in it to form a trap when the vapor supply pressure is sufficient to open the check valve. The flame-arresting discharge head is combined with a flare stack assembly at the vapor discharge opening. The vapor inlet-liquid seal entry feature permits the free passage of a gas therethrough until such time as an interruption of flow occurs whereupon the check valve closes and the liquid within the liquid equalization line rises and fills the gas entry line thus in eflect producing a liquid seal which prevents any back flow of gas through the vapor line. Further, blowing of the liquid seal is almost impossible because where slugging or a sudden rapid flow of vapor to the stack occurs the liquid within the liquid seal is displaced into the 'bottom of the seal drum permitting free flow of vapor through the vapor entry line, the check valve and through the liquid loop. Where a malfunction of the check valve occurs vapor is free to pass through the liquid loop.

FIGURES 1-3 show a seal drum assembly for use between a header wherein gases or vapors are collected, and a flare stack. FIGURE 4 shows the combination of the seal drum assembly and the flare stack. Vapors or gases thus pass through line 10 into the seal drum assembly and out of the assembly through the exit line 14 and through lines 22, 23 and 24 into flare stack 25. Ignition of the vapors is insured by pilot light 26. The seal drum assembly includes a seal drum 19, a vapor inlet-liquid seal entry feature including a vapor loop seal 17 joined in parallel to a ball check valve 16 and to a liquid loop 18. The ball check valve 16, including a cage 20, ball 15 and a ball check seat 13, and the line 21 adjoining the check valve 16 is largely contained within the confines of the seal drum 19. The liquid equalization line or liquid loop 18 is operatively joined to the vapor loop seal 17 and to the seal drum 19.

When no gas flows through the line 10, or at no-flow conditions as shown in FIGURE 1, the liquid level 11 in both the seal drum 19 and gas inlet line 10 is several inches below the ball check seat 13 and fills both the vapor loop 17 and liquid loop 18. A liquid seal between the gas inlet line 10 and the exit line 14 to the flare is 3 thereby provided. The size of the ball 15 and its weight are set to provide a fixed back-pressure on the gas inlet line 10. The vapor loop 17 opens into the branched member at a point where the liquid pressure is greater than the back pressure of check valve 15 thus preventing vapor from passing through the liquid loop during normal operations.

When the gas or vapor starts to flow as in FIGURE 2, the back-pressure imposed by the ball 15 causes liquid to be displaced from the vapor seal loop 17 and into the liquid loop 18 and into the seal drum 19. The vapor then passes through exit line 14 and through lines 22, 23 and 24 into flare stack 25. Ignition of the vapors is insured by pilot light 26. As long as vapor continues to flow, the vapor seal loop 17 will be free of liquid and essentially no fluid will be vaporized. The relative sizes of the vapor line 10, the vapor seal 17 and the backpressure provided by liquid seal line 18 Will assure that vapor does not flow through the liquid seal line 18 during normal operations and thus slug liquid to the flare stack.

When vapor flow stops, the ball check 15 will reseat and the vapor seal loop 17 will refill with liquid. In the event of a flash back from the flare stack, the ball check 15 will be slammed shut to prevent the propagation of flame past this point should it occur because of back mixing of air with hydrocarbon vapors in the flare stack. Liquid from line 18 reseals vapor seal line 17 and seals flame propagation through the liquid loop 18.

FIGURE 3 shows the displacement of the liquid from the vapor loop 17 and liquid loop 18 and into the seal drum 19 to permit passage of vapor through the liquid loop 18 when the ball seal 15 is stuck, not permitting the flow of vapor through the ball check valve 16.

To illustrate the invention the following non-limiting example is given.

Into a seal drum assembly as shown and described, having kerosene (flash point, 150 F.) as the sealing liquid, is charged an acid gas or vapor of the following approximate weight composition:

Nitrogen Trace Ethyl chloride 20 Hydrogen chloride l Ethylene 65 Ethane The ball 15 of the ball-check valve 16, set to provide a back-pressure on the gas inlet line of 0.75 pound per square inch, is moved upward and the kerosene within the vapor loop seal 17 is displaced to allow passage of the vapor through loop seal 17 and line 21. The vapors pass into seal drum 19, out line 14 and through lines 22, 23 and 24 into flare stack 25 where they are ignited by pilot light 26. When the flow ceases the ball is reseated and there is no flash back beyond this point or:

through the liquid seal.

When the flow of vapor through the ball-check valve 16 is suddenly and severely increased the vapor flows through the vapor seal loop 17, line 21 and through the liquid loop 18 while the kerosene is displaced to the bottom of the seal drum 19. The kerosene is not displaced out of the seal drum 19, and when the pressure returns to normal the kerosene flows back into and fills the liquid loop 18 preventing further passage of vapor therethrough, and does not permit the propagation of flame beyond this point.

It is quite obvious that any of an extremely wide variety of sealing liquids can be employed in the device described without departing from the spirit and scope of the invention. Preferably however hydrocarbon liquids are selected which have a very low freezing point, reasonably low volatility, i.e., from about 100 F. to about 300 F., are non-corrosive and inexpensive. Kerosene and naphthas are extremely useful compounds.

Further, it is apparent that the apparatus itself is susceptible to considerable variation and applicant does not desire to be limited except within the spirit and scope of the appended claims.

Having described the invention what is claimed is:

1. A flame-arresting discharge head for combustible vapors, said head having a liquid seal drum with a vapor discharge opening at its upper portion, a liquid seal loop trap opening into the lower portion of the drum, a vapor supply loop extending through the bottom of the drum and opening within the drum at a height above that at which the liquid seal trap loop opens so that the opening of the vapor supply loop is not covered by liquid from the liquid trap, the vapor supply loop extending downwardly from the bottom of the seal drum and joining the liquid seal loop trap at a branched connection, one branch extending downwardly for a distance and then upwardly to form the liquid seal trap loop and the other branch extending laterally for connection to a vapor supply above the level of the bottom of the seal drum, and a check valve closing the, opening of the vapor supply loop within the seal drum against downward passage of flame and permitting upward travel of vapor through the lastmentioned opening only when the vapor is supplied under a pressure suificieut to open the check valve, said pressure being also suflicient to expel the trap liquid from the portion of the vapor supply loop above the branched connection, the liquid seal trap loop extending far enough below the branched connection so that liquid remains in it to form a trap when the vapor supply pressure is sufficient to open the check valve.

2. The discharge head of claim 1 in which kerosene is the liquid of the liquid seal trap loop.

3. A flare stack for burning excess refinery vapors, said stack having a discharge head according to claim 1.

4. A device for disposing of combustible vapors, comprising a flame-arresting discharge head, said head being a liquid seal drum with a vapor discharge opening at its upper portion, a liquid seal loop trap opening into the lower portion of the drum, a vapor supply loop extending through the bottom of the drum and opening within the drum at a height above that at which the liquid seal trap loop opens so that the opening of the vapor supply loop is not covered by liquid from the liquid trap, the vapor supply loop extending downwardly from the bottom of the seal drum and joining the liquid seal trap at a branched connection, one branch extending downwardly for a distance and then upward to form the liquid seal trap loop and the other branch extending laterally for connection to a vapor supply above the level of the bottom of the seal drum, and a check valve closing the opening of the vapor supply loop within the seal drum against downward passage of flame and permitting upward travel of vapor through the last mentioned opening only when the vapor is supplied under a pressure suflicient to open the check valve, said pressure being also suflicient to expel the trap liquid from the portion of the vapor supply loop above the branched connection, the liquid trap loop extending far enough below the branched connection so that liquid remains in it to form a trap when the vapor supply pressure is sufiicient to open the check valve, said liquid seal being a liquid hydrocarbon; and a flare-stack, the lower portion of which is connected to the vapor discharge opening of the liquid seal drum.

References Cited by the Examiner Webster et al; 137247.35 X

ISADOR WEIL, Primary Examiner, 

1. A FLAME-ARRESTING DISCHARGE HEAD FOR COMBUSTIBLE VAPORS, SAID HEAD HAVING A LIQUID SEAL DRUM WITH A VAPOR DISCHARGE OPENING AT ITS UPPER PORTION, A LIQUID SEAL LOOP TRAP OPENING INTO THE LOWER PORTION OF THE DRUM, A VAPOR SUPPLY LOOP EXTENDING THROUGH THE BOTTOM OF THE DRUM AND OPENING WITHIN THE DRUM AT A HEIGHT ABOVE THAT IT WHICH THE LIQUID SEAL TRAP LOOP OPENS SO THAT THE OPENING OF THE VAPOR SUPPLY LOOP IS NOT COVERED BY LIQUID FROM THE LIQUID TRAP, THE VAPOR SUPPLY LOOP EXTENDING DOWNWARDLY FROM THE BOTTOM OF THE SEAL DRUM AND JOINING THE LIQUID SEAL LOOP TRAP AT A BRANCHED CONNECTION, ONE BRANCH EXTENDING LATERALLY FOR CONNECTION TO A VAPOR SUPPLY ABOVE THE LEVEL OF THE BOTTOM OF THE SEAL DRUM, AND A CHECK VALVE CLOSING THE OPENING OF THE VAPOR SUPPLY LOOP WITHIN THE SEAL DRUM AGAINST DOWNWARD PASSAGE OF FLAME AND PERMITTING UPWARD TRAVEL OF VAPOR THROUGH THE LASTMENTIONED OPENING ONLY WHEN THE VAPOR IS SUPPLIED UNDER A PRESSURE SUFFICIENT TO OPEN THE CHECK VALVE, SAID PRESSURE BEING ALSO SUFFICIENT TO EXPEL THE TRAP LIQUID FROM THE PORTION OF THE VAPOR SUPPLY LOOP ABOVE THE BRANCHED CONNECTION, THE LIQUID SEAL TRAP LOOP EXTENDING FAR ENOUGH BELOW THE BRANCHED CONNECTION SO THAT LIQUID REMAIN IN IT TO FORM A TRAP WHEN THE VAPOR SUPPLY PRESSURE IS SUFFICIENT TO OPEN THE CHECK VALVE. 